1. Field of the Invention
The present invention relates to a brushless motor drive device that performs switching determination of energization modes of a three-phase brushless motor according to a sensorless method, and a drive method thereof.
2. Description of Related Art
Japanese Laid-open Patent Publication No. 2009-189176 discloses a drive system of a synchronous electric motor that detects a pulse induced voltage of a non-energized phase induced by a pulse voltage, in a three-phase synchronous electric motor, and compares the pulse induced voltage with a reference voltage to sequentially switch the energization modes according to the comparison result.
The pulse induced voltage of the non-energized phase is detected while a pulse voltage is applied to two phases. However, immediately after start of voltage application, the pulse induced voltage oscillates. Therefore, if a duty ratio of the pulse voltage is small, the level of the pulse induced voltage is detected in a state with the pulse induced voltage oscillating, and hence, energization mode switching timing may be erroneously determined.
Moreover, a magnitude of the pulse induced voltage in the non-energized phase changes according to the duty ratio of the pulse voltage. Consequently, if the duty ratio is small, the voltage falls below a voltage detection resolution, and hence, determination of the energization mode switching timing may not be performed.